1. Field of the Invention
The present invention relates to an unmanned vehicle used, for example, in an unmanned conveying system. In particular, it relates to a travel control device for an unmanned vehicle.
2. Description of the Related Art
Unmanned vehicles are used in unmanned conveying systems in, for example, factories and warehouses. Most such unmanned vehicles are now electronically controlled and automatically travel at a constant speed along a predetermined path, and because the vehicle has no driver or attendant, an emergency stop means is incorporated in these unmanned vehicles. A typical emergency stop means is illustrated in FIGS. 8 and 9 of the attached drawings, wherein an unmanned vehicle 31 automatically travels along a predetermined travel path in the direction of the arrow F, and a known travel control device therefor includes a non-contact type obstacle sensor 32 (for example, an ultrasonic sensor) and a contact type obstacle sensor 33 (for example, a bumper sensor) arranged at the front of the vehicle, respectively, to stop the unmanned vehicle 31 in response to a detection signal output by the sensors 32 and 33.
The non-contact type obstacle sensor 32 detects an obstacle M (for example, a person) at a certain distance "d" (for example, 1 meter) from the unmanned vehicle 31, an emergency stop of the unmanned vehicle 31 is carried out as soon as the obstacle M is detected, and the unmanned vehicle 31 is automatically restarted when the output of the obstacle detection signal ceases. Also, the contact type obstacle sensor 33 detects an obstacle M upon a contact thereof with the contact type obstacle sensor 33, an emergency stop of the unmanned vehicle 31 is carried out, and the unmanned vehicle 31 is restarted when the output of the obstacle detection signal ceases and a manual start switch (not shown) is operated. In this manner, a safe movement of the unmanned vehicle 31 during travel is ensured by the emergency stop procedure based on a detection of signals output by the non-contact type and contact type obstacle sensors 32 and 33.
Nevertheless, a problem arises with unmanned vehicle 31 controlled by such a known travel control device when such a vehicle is part of a conveying system of an assembly line in a machine manufacturing factory. Namely, in an assembly line in a machine manufacturing factory, operators frequently approach and move around the unmanned vehicle 31, to unload a workpiece W carried by the unmanned vehicle or to attach parts to a workpiece W on the unmanned vehicle 31, and thus frequent emergency stops of the unmanned vehicle 31 are made, based on the detection of signals output by the non-contact type and contact type obstacle sensors 32 and 33.
In particular, detections by the non-contact type obstacle sensor 32 frequently cause the unmanned vehicle 31 to stop, and these frequent stops of the unmanned vehicle 31 have an adverse affect on sequential operations such as assembly work at an assembly line. Further, when a plurality of such unmanned vehicles 31 move together at predetermined intervals, frequent stops of the unmanned vehicle 31 cause irregular intervals to appear between the sequentially travelling unmanned vehicles 31, and thus problems arise in a conveying system in which articles are required to be conveyed at constant intervals.